Porcelain Build Up

Lecture Overview

• Instructor: Dr. Dina Aboulftouh
• Title: Lecturer of Fixed Prosthodontics
• Institution: Faculty of Dental Medicine for Girls, Al Azhar University

Steps in Porcelain Build Up

1. Mixing
2. Application
3. Condensation
4. Firing
5. Shaping & Glazing
   

1. Mixing

• Material Components:
    - Dental ceramics are supplied as different shaded powders combined with a liquid binder.
    - Common binders include:
      - Distilled water
      - Water-based glycerin (used in Dentin & Enamel Porcelain)
      - Propylene glycol (used in Aluminous Core)
• Mixing Process:
    - Selected shade powder is combined with a liquid to create a creamy mix.
    - Porcelain is then collected as a bead from the edge of the mixed solution.

2. Application

• Purpose of Application:
    - The creamy mix is applied on the die using a brush or spatula in successive layers until the desired shape and contour are achieved.
• Application Methods:
    1. Platinum Foil Technique (used for Traditional Feldspathic Porcelain Jacket Crown)
    2. Refractory Die Technique (used for Aluminous Core)
• Layers in an All-Ceramic Crown:
    - Core: high-strength porcelain
    - Body: dentine
    - Incisal: enamel
    - Glaze: final layer
• Specific brushes are utilized for porcelain buildup depending on the application stage.
    - Application includes gingival dentine porcelain followed by completed dentine porcelain buildup and enamel porcelain application.

3. Condensation

• Definition:
    - The process involves densely packing and removing excess water from the working porcelain mass after it has been molded into the desired shape.
• Purpose of Condensation:
    1. Removal of Excess Water
    2. Decrease Firing Shrinkage
    3. Decreased Porosity
    4. Increased Strength of Porcelain
    5. Easily Adapted Paste to Required Form
• Methods of Condensation:
    - Vibration: Applying gentle vibration on the die and removing excess water with absorbent tissue paper.
    - Brush (Capillary Attraction): Applying dry powder to a small area of wet porcelain.
    - Spatulation: Smoothening the wet porcelain with a spatula.
    - Gravitation: Removing excess water using absorbent tissue paper.
    - Ultrasonic Condensation:
      - Advantages include:
        1. Time-saving
        2. Shrinkage reduction to below 5%
        3. Reduction of fluid content in layered ceramics.
• Preheating Procedure:
    - The condensed porcelain mass is preheated at approximately 650°C in front of or below a muffle furnace for low-fusing porcelain to dissipate residual water vapor.
• Risks of Improper Placement:
    - Directly placing the condensed mass into the furnace can lead to rapid steam production, which may create voids or fracture parts of the mass.

4. Firing

• Definition of Sintering:
    - Sintering occurs in a furnace to fuse powder particles, promoting the flow of materials and creating glass bridges among unfused particles to form a continuous mass.
• Restoration:
    - Following the porcelain buildup, the material must undergo a firing process for proper finishing.

5. Glazing

• Description of Glaze Layer:
    - The glaze layer is the final, extremely thin coating that provides a smooth surface and translucency, imitating the appearance of enamel or dentin.
• Properties and Function of Glaze:
    - Surface glaze strengthens ceramics by forming a low-expansion surface layer during a high-temperature firing process.
    - Upon cooling, the low-expansion glaze compresses the ceramic surface and minimizes the depth and width of any surface flaws.
• Glass Flow Mechanics:
    - The process involves the surface glass flow that may occur during the final bake (self-glaze or auto glaze technique) or through applying a low-fusing glass (overglaze).
• Types of Glaze Techniques:
    1. Self-Glaze: Naturally formed vitrified layer that does not significantly enhance flexural strength.
    2. Over Glaze: Clear, colorless low-fusing glass powder is applied to the fired crown surface and refired.
    3. Add-on Glaze: Incorporates color pigments for contour correction or adjusting contact points after the initial glaze application.

Conclusion

• In summary, the process of porcelain buildup in fixed prosthodontic practices involves meticulous preparation, application, and finalization through firing and glazing techniques. Understanding each step and its purpose is critical for achieving successful dental restorations.